On 11/9/21 12:32 PM, Changliang Wu wrote:
> This change is meant to add a control for forwarding skb from local.
> By default, ip forward will not receive the pakcet to/from the local.
> But in some special cases, for example:
> -
> | ovs-bridge gw-port | <----> kube-proxy(iptables) |
> -
> Ovs sends the packet to the gateway, which requires iptables for nat,
> such as kube-proxy (iptables), and then sends it back to the gateway
> through routing for further processing in ovs.
>
> Signed-off-by: Changliang Wu <[email protected]>
> ---
> include/net/netns/ipv4.h | 1 +
> net/ipv4/af_inet.c | 1 +
> net/ipv4/ip_forward.c | 6 +++---
> net/ipv4/sysctl_net_ipv4.c | 7 +++++++
> 4 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
> index 2f65701..0dbe0d6 100644
> --- a/include/net/netns/ipv4.h
> +++ b/include/net/netns/ipv4.h
> @@ -94,6 +94,7 @@ struct netns_ipv4 {
> u8 sysctl_ip_no_pmtu_disc;
> u8 sysctl_ip_fwd_use_pmtu;
> u8 sysctl_ip_fwd_update_priority;
> + u8 sysctl_ip_fwd_accept_local;
> u8 sysctl_ip_nonlocal_bind;
> u8 sysctl_ip_autobind_reuse;
> /* Shall we try to damage output packets if routing dev changes? */
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index 0189e3c..b5dc205 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1844,6 +1844,7 @@ static __net_init int inet_init_net(struct net *net)
> */
> net->ipv4.sysctl_ip_default_ttl = IPDEFTTL;
> net->ipv4.sysctl_ip_fwd_update_priority = 1;
> + net->ipv4.sysctl_ip_fwd_accept_local = 0;
> net->ipv4.sysctl_ip_dynaddr = 0;
> net->ipv4.sysctl_ip_early_demux = 1;
> net->ipv4.sysctl_udp_early_demux = 1;
> diff --git a/net/ipv4/ip_forward.c b/net/ipv4/ip_forward.c
> index 00ec819..06b7e00 100644
> --- a/net/ipv4/ip_forward.c
> +++ b/net/ipv4/ip_forward.c
> @@ -95,9 +95,6 @@ int ip_forward(struct sk_buff *skb)
> if (skb->pkt_type != PACKET_HOST)
> goto drop;
>
> - if (unlikely(skb->sk))
> - goto drop;
> -
> if (skb_warn_if_lro(skb))
> goto drop;
>
> @@ -110,6 +107,9 @@ int ip_forward(struct sk_buff *skb)
> skb_forward_csum(skb);
> net = dev_net(skb->dev);
>
> + if (unlikely(!net->ipv4.sysctl_ip_fwd_accept_local && skb->sk))
> + goto drop;
> +
Why moving the check further down instead of initializing dev_net(skb->dev) earlier?
What about ip6_forward()? Same issue exists there too I presume?
> /*
> * According to the RFC, we must first decrease the TTL field. If
> * that reaches zero, we must reply an ICMP control message telling
> diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
> index 97eb547..d95e2e3 100644
> --- a/net/ipv4/sysctl_net_ipv4.c
> +++ b/net/ipv4/sysctl_net_ipv4.c
> @@ -756,6 +756,13 @@ static int proc_fib_multipath_hash_fields(struct ctl_table *table, int write,
> .extra2 = SYSCTL_ONE,
> },
> {
> + .procname = "ip_forward_accept_local",
> + .data = &init_net.ipv4.sysctl_ip_fwd_accept_local,
> + .maxlen = sizeof(u8),
> + .mode = 0644,
> + .proc_handler = proc_dou8vec_minmax,
> + },
> + {
> .procname = "ip_nonlocal_bind",
> .data = &init_net.ipv4.sysctl_ip_nonlocal_bind,
> .maxlen = sizeof(u8),
>